More efficient structural cell for facilitating tree root growth

ABSTRACT

A structural cell system for supporting hardscape, allowing tree root growth, and managing stormwater underneath the hardscape. The system may include: a base having a plurality of receptacles and a plurality of support members interconnecting the receptacles; a plurality of legs each sized and shaped to be attachable to the base within one of the receptacles so as to extend from the base, and to be attachable to another of the legs so that pairs of legs attached to each other collectively extend from the base; and a top attachable to the legs. Outer edges of the base, the top, and the legs attached thereto define a volume, and are configured to support at least that portion of the hardscape overlying the top as well as a commercial vehicle traffic load thereon, while maintaining soil in a substantially uncompacted state throughout at least approximately ninety percent of the volume.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/686,573 filed Aug. 25, 2017 and titled “More Efficient StructuralCell For Facilitating Tree Root Growth”, which is a divisional of U.S.patent application Ser. No. 14/684,214 filed Apr. 10, 2015, now U.S.Pat. No. 9,775,303 and titled “More Efficient Structural Cell forFacilitating Tree Root Growth”, each of which is incorporated herein byreference in its entirety.

BRIEF DESCRIPTION

This invention relates generally to tree growth technology. Morespecifically, this invention relates to structural cells for moreefficiently facilitating tree root growth and water retention.

BACKGROUND

The design of many modern dense urban landscapes often calls for theplacement of trees within paved-over areas or areas covered by otherhardscapes. In particular, such designs often call for trees to beplaced in close proximity to roads, sidewalks, and other load bearingpathways. However, the design and construction methods of these pathwaysand the loads they carry often compact the soil underneath to such anextent that it is often difficult for tree roots to sufficientlypenetrate the soil. As a result, trees planted in close proximity tothese hardscapes may not survive or grow to the full extent envisioned.

Various solutions to this problem have been proposed. For example,structural cell systems such as those disclosed in U.S. Pat. Nos.7,080,480 and 8,065,831, which are both hereby incorporated by referencein their entireties and for all purposes, have been designed tofacilitate the growth of trees near hardscapes, while allowing for soilaeration, water drainage, and the like. It is, however, desirable toimprove various aspects of such cells. Accordingly, continuing effortsexist to make such structural cells support hardscapes better, whileimproving the manufacturability and other characteristics of such cells.

SUMMARY OF THE INVENTION

The invention can be implemented in numerous ways. Accordingly, variousembodiments of the invention are discussed below.

In one embodiment, a structural cell system for supporting hardscape andallowing tree root growth and managing stormwater underneath thehardscape comprises: a base having a plurality of receptacles and aplurality of support members interconnecting the receptacles; aplurality of legs each sized and shaped to be attachable to the basewithin one of the receptacles so as to extend from the base, and to beattachable to another of the legs so that pairs of legs attached to eachother collectively extend from the base; and a top attachable to thelegs. Outer edges of the base, the top, and the legs attached theretodefine a volume, and are configured to support at least that portion ofthe hardscape overlying the top as well as a commercial vehicle trafficload thereon, while maintaining soil in a substantially uncompactedstate throughout at least approximately ninety percent of the volume.

Outer edges of the receptacles may extend beyond outer edges of thesupport members.

The base and the legs may each comprise an unreinforced plastic, such ashigh density polyethylene (HDPE).

The base, the top, and the legs attached thereto may be sized and shapedto support a load of at least approximately 15 psi across substantiallythe entire top.

At least two of the receptacles may lie along a first direction, and atleast two of the receptacles may lie along a second direction differentfrom the first direction. Also, each of the legs may have across-sectional shape having protrusions, the protrusions arranged sothat, when each of the legs is attached to a receptacle, its protrusionsextend in the first and second directions.

The plurality of legs may comprise legs having a first length and legshaving a second length shorter than the first length. Each pair of legsmay comprise a leg having the first length and a leg having the secondlength.

The base may be configured so that plural ones of the bases arestackable in a vertical direction so as to be substantially coupled in alateral direction perpendicular to the vertical direction, and so as tobe substantially uncoupled in the vertical direction; and the top may beconfigured so that plural ones of the tops are stackable in the verticaldirection so as to be substantially coupled in the lateral direction andsubstantially uncoupled in the vertical direction.

The system may further comprise a bioretention system positioned withinthe structural cell system; and tree roots extending into thebioretention system, the tree roots being from a tree positionedproximate to the structural cell system.

The base, the associated legs, and the top may collectively comprise asingle structural cell, and the structural cell may have no mechanismfor coupling to another one of the structural cells.

In another embodiment, a method of facilitating the growth of a treecomprises: placing a plurality of structural cells side by side andadjacent to each other, so that the structural cells are substantiallyuncoupled to each other and so that the structural cells substantiallysurround the rootball of a tree. Each structural cell may comprise: abase having a plurality of receptacles and a plurality of supportmembers interconnecting the receptacles; a top; and a plurality of legsaffixing the base to the top. Outer edges of the base, the top, and thelegs affixed thereto define a volume, and are configured to support atleast that portion of a hardscape overlying the top as well as acommercial vehicle traffic load thereon, while maintaining soil in asubstantially uncompacted state throughout at least approximately ninetypercent of the volume.

The method may further comprise filling the cells with a substantiallyloosely compacted soil, so as to allow roots of the tree to grow intothe soil within the structural cells while simultaneously providingstorage and pollutant removal of stormwater.

Each receptacle may be connected to the top by a pair of interconnectedones of the legs.

The filling the cells may further comprise filling the cells withmaterial layers so as to form a bioretention system within the cells,each of the material layers being substantially uncompacted so as toallow roots of the tree to grow into the bioretention system within thecells.

Other aspects and advantages of the invention will become apparent fromthe following detailed description taken in conjunction with theaccompanying drawings which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference should be made tothe following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates operation of an exemplary structural cell system ofthe invention;

FIG. 2A illustrates an isometric detail view of an assembled structuralcell of the invention;

FIG. 2B is a side view of the assembled structural cell of FIG. 2A;

FIG. 2C is a cross-section view taken along line I-I′ of FIG. 2B;

FIG. 3A is a plan view of the base of the structural cell of FIG. 2A;

FIGS. 3B and 3C are side views of the base of FIG. 3A;

FIG. 4A is an isometric view of one embodiment of a leg of thestructural cell of FIG. 2A, where in this embodiment the leg is a longerleg;

FIG. 4B is a side view of the leg of FIG. 4A;

FIG. 4C is a cross-section view of a center portion of the leg of FIG.4A;

FIG. 5A is an isometric view of another embodiment of the leg of thestructural cell of FIG. 2A, where in this embodiment the leg is ashorter leg;

FIG. 5B is a side view of the leg of FIG. 5A;

FIG. 5C is a cross-section view of a center portion of the leg of FIG.5A;

FIG. 6A is a plan view of the deck of the structural cell of FIG. 2A;

FIGS. 6B and 6C are side views of the deck of FIG. 6A;

FIG. 7A is an isometric detail view of an assembled structural cell,using both longer legs and shorter legs;

FIG. 7B is a side view of the structural cell of FIG. 7A;

FIG. 7C is a cross-section view taken along line II-II′ of FIG. 7B;

FIG. 8A is an isometric detail view of an assembled structural cell,using only shorter legs;

FIG. 8B is a side view of the structural cell of FIG. 8A;

FIG. 8C is a cross-section view taken along line III-III′ of FIG. 8B;

FIG. 9A is an isometric detail view of stacked bases constructed inaccordance with embodiments of the present invention;

FIG. 9B is a side view of the stacked bases of FIG. 9A;

FIG. 9C is a cross-section view taken along line IV-IV′ of FIG. 9B;

FIG. 10A is an isometric detail view of stacked decks constructed inaccordance with embodiments of the present invention;

FIG. 10B is a side view of the stacked decks of FIG. 10A; and

FIG. 10C is a cross-section view taken along line V-V′ of FIG. 10B.

Like reference numerals refer to corresponding parts throughout thedrawings. The various Figures are not necessarily to scale.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In one aspect, the invention relates to structural cell systems that areplaced beneath hardscape. The cells are strong enough to structurallysupport the hardscape, effectively bearing its weight along with theweight of any load it carries. Furthermore, even though the cells arestrong enough to offer structural support of a hardscape, the cells arealso designed to be relatively lightweight and open, allowingapproximately 90% of their volume, or more, to be free volume that cancontain uncompacted soil, tree roots, utilities, and the like. Some ofthe components of the cell systems are stackable for bettertransportability. The cells achieve these attributes through a designthat includes a bottom frame, attachable support members, and anattachable deck or top. The various components of the cells are designedto utilize less material relative to the cells of U.S. Pat. Nos.7,080,480 and 8,065,831, while also being able to support the load ofoverlying hardscape and commercial vehicles yet being made of a moreinexpensive material. Furthermore, the legs are attachable to each otherso that individual cells can be made of multiple sizes, some of whichare taller than the individual cells of U.S. Pat. Nos. 7,080,480 and8,065,831. This allows a single layer of cells to take the place ofmultiple layers of the previous cells, thus further reducing the amountof material used.

FIG. 1 illustrates an exemplary application of the structural cells ofthe invention. Here, a tree 10 grows its roots in the soil 50 underneatha hardscape 20 and layer of aggregate 30. Structural cells 40 arestacked between the hardscape 20 and aggregate 30 above, and foundation60 below. The cells 40 are sufficiently rigid that they structurallysupport the weight of the hardscape 20, aggregate 30, and any loadsabove (e.g., cars, pedestrians, etc.), transferring it to the foundation60 rather than the soil 50. This maintains the soil 50 within thestructural cells 40 in a relatively uncompacted state, allowing rootsfrom the tree 10 to grow therethrough as shown. In addition, therigidity of the cells 40 allows a relatively small number of supportmembers to bear structural loads. In this manner, the cells 40 maintaina large amount of continuous open volume within, free of excessivenumbers of support members that take up space and prevent large treeroots from growing therethrough. Space is left between adjacentstructural cells 40 for ease in removing/repairing individual cells 40without disturbing the rest.

In some embodiments, the structural cells 40 are configured to satisfy anumber of constraints. For example, the cells 40 should be composed of amaterial capable of withstanding an underground environment that cancontain water. This material should also be of sufficient strength tosupport a hardscape 20, aggregate 30, and their associated loads. Insome embodiments, it is preferable for the cells 40 to support loads inaccordance with known AASHTO (American Association of State Highway andTransportation Officials) H-20 load requirements. In addition, the cells40 are to be configured to be stackable side by side, as shown in FIG.1, without interlocking or coupling together. That is, while adjacentcells 40 may contact each other and thus be subject to frictional forcestherebetween, they are not otherwise coupled to each other. For example,adjacent cells 40 are not attached to each other, and cells 40 do notcontain any features allowing them to be connected to any other cells40. In this manner, cells 40 can be relatively easily removed in theevent that any features below or within them, such as utilities, servicelines, or the like, must be accessed for maintenance or repair. Leavingcells 40 unconnected to each other also acts to localize the failures ofany individual cells 40, so that the failure of one cell 40 does notcompromise any other cells 40, and the failed cell 40 can be relativelyeasily replaced by simply removing it and adding another in its place.Finally, the various component parts of cells 40 may be designed to beinjection-moldable, although embodiments of the invention contemplateany method of fabricating any part of the cells 40.

These constraints are satisfied by the structural cell design of FIG.2A, which illustrates further details of the structural cells 40 ofFIG. 1. In FIG. 2A, the structural cell 40 has a base or lower portion100, legs or vertical supports 110, and a top, deck, or upper portion120. The base 100, legs 110, and deck 120 are fabricated separately andassembled to form the cell 40 shown.

In the embodiment shown, the assembled cell 40 is generally rectangular,with three support members 110 along each of its longer sides for atotal of six vertical supports 110. More specifically, a verticalsupport 110 is located at each corner of the cell 40, with twoadditional vertical supports 110 located inbetween. The lower frame 100is also relatively thin and therefore pliable to a degree, so as toconform to small irregularities in the foundation 60. It can be observedthat the cell 40 leaves the volume within largely unobstructed, i.e.,free of excessive numbers of support members, allowing large roots andother large-sized objects to be placed within. This yields significantadvantages, as cells 40 not only contain relatively large amounts ofopen space, but this open space is also easily accessible forpenetration by roots (such as those of tree 10) or other objects. Thus,not only is space available for roots and other objects, but they canalso grow into, or be placed within, the cells in a relatively unimpededfashion. Cells 40 can thus be used in connection with even very largetrees with large root systems, as the cells 40 offer very little in theway of obstructions to impede the growth of even large rootstherethrough. This creates cells 40 with relatively large openstructures that can be easily accessed and thus, for example, are easilyfilled with soil, in contrast to cells with excessive numbers of supportmembers that inhibit the placement of soil or other objects within.

As can be seen in FIGS. 2B and 2C, each cell 40 has two rows of threelegs 110 each, with three legs 110 positioned evenly along each longerside of cell 40, and two legs 110 positioned at each end of each shorterside of cell 40. As will be described further below, bottom ends of thelegs 110 are inserted into recesses in the base 100, and the deck 120 isapplied to the top ends of the legs 110.

FIGS. 3A-3C illustrate further details of the base 100. In thisembodiment, the base 100 is a rectangular framelike structure with sixrecesses 200 interconnected by outer longitudinal supports 210 and innerlongitudinal supports 230, although any size and shape of base 100 iscontemplated. The recesses 200 are each sized and shaped to accommodatea leg 110, which can turn and lock into its recess 200. Outer edges ofthe outer longitudinal supports 210 collectively form a perimeter aroundthe base 100, with inner longitudinal supports 230 also connectingadjacent recesses 200 while being located inside, and spaced apart from,outer longitudinal supports 210. Outer edges 220 of recesses 200protrude beyond the perimeter formed by the outer edges of the outerlongitudinal supports 210. That is, the recesses 200 are positioned toat least partially extend beyond the outer edges of outer longitudinalsupports 210.

The base 100 also has crossbars 240 connecting diagonally-adjacent pairsof recesses 200. That is, crossbars 240 connect recesses 200 at thecorners of base 100 to recesses 200 located at the middle of the longersides of base 100. Pairs of crossbars 240 intersect, and footpads 250are placed at their intersections. Footpads 250 are formed by placingcurved supports 260 at the intersections of pairs of crossbars 240, andcan be used by workers when constructing the assemblies of cells 40shown in FIG. 1. For example, footpads 250 allow workers safe places tostep when the bases 100 are already placed below ground, so that theworkers do not step on other more fragile parts of cells 40. Thefootpads 250 are shown as circular and are sized to support a human footin a work boot, although various embodiments contemplate any size andshape for the footpad 250. Crossbar 250 is also located between the tworecesses 200 placed at the middle of the longer sides of the base 100,so as to add extra support in the vertical direction of FIG. 3A.

It should be noted that the configuration of FIG. 3A yields significantsavings in material over conventional structural cell bases. Forexample, as noted previously, the outer longitudinal supports 210 areset inward from the outer edges 220 of recesses 200, resulting in lessmaterial used as compared to conventional structural cells whose outersupports extend parallel to their recesses (making them longer and thususing more material), while still maintaining structural integrity.Also, the present embodiment utilizes two supports 210, 230 separated bya space inbetween, rather than a single wider, solid support. This alsoresults in material savings. Likewise, the footpads 250 are configuredas relatively thin outer curved supports 260 surrounding empty space,save for that portion of crossbars 240 extending within. The significantamount of empty space thus also provides a footpad made from arelatively small amount of material.

The legs or vertical supports 110 are not limited to the length shown inFIG. 2A, but instead can be any length. In particular, one embodiment ofthe invention contemplates legs of two different lengths. In thismanner, cells of at least three different heights can be made: a shortercell with short legs, a medium-height cell with the longer legs, and atall cell with each vertical support made of a longer leg connected to ashorter leg. This allows for the flexibility to make cells of differentheights, so that the same component parts can be used to assemble cellssuitable for many different applications.

FIGS. 4A-4C illustrate further details of a longer leg. Here, longer leg300 includes ends with features 310 and 330 for connection to the base100 and top/another leg respectively, as well as a central portion withlongitudinal protrusions 320. The features 310, 330 are featuresallowing for turn and lock connection to the base 100 and top/other leg.For example, the features 310, 330 can be slots and a corresponding pinor other extension sized to fit into the slot so that turning the legsecures the pin in the slot. The features 310, 330 are configured toallow turn and lock connection to both the base 100 and another leg orthe top 120. For instance, the lower end of leg 300 has slots asfeatures 310, while the upper end of leg 300 has pins or extensions asfeatures 330, while the recesses 200 have pins or extensions, and thecorresponding portions of the top 120 have snap fit joints. This allowsthe leg 300 to be turned and locked into place within a recess 200 ofbase 100, whereupon either the lower end of another leg can be turnedand locked onto the upper end of leg 300, or the top 120 can be snappedinto place on the upper end of leg 300. If another leg is attached tothe upper end of leg 300, the top 120 is snapped onto the upper end ofthat added leg.

The longitudinal protrusions 320 extend outward, adding to the radius ofthe leg 300 and thus improving the strength of the leg 300. Inparticular, the protrusions 300 improve the bending stiffness andbuckling strength of the leg 300, as would be understood by one ofordinary skill in the art. The protrusions 320 can be oriented so thatthe center of each protrusion 320, i.e. the point of maximum height ordistance from the central axis of leg 300, is oriented parallel to oneof the sides of base 100, i.e. in FIG. 3A, a line drawn through thecenters of two opposing protrusions 320 of a leg 300 is oriented eitherhorizontally or vertically, along either the longer side or the shorterside of the leg 300. It has been found that this orientation providesdesirable resistance to buckling. However, it should be noted that anynumber and orientation of protrusions 300 is contemplated. Also, theprotrusions 320 can be of any cross-sectional shape. The shape of eachprotrusion 320 is not limited to the curved or domelike cross-sectionalshape shown in FIG. 4C, but can be any cross-sectional shape thatimproves the strength of its leg 300.

FIGS. 5A-5C illustrate further details of a shorter leg. Similar to thelonger leg 300, shorter leg 400 has features 410, 430 that are similarto the respective features 310, 330 of longer leg 300. That is, features410, 430 can be slots and pins/extensions respectively, which allow theshorter leg 400 to lock within recesses 200 of base 100, and to besnapped onto the top 120. Also, longitudinal protrusions 420 are shaped,and act, similar to protrusions 320 of leg 300, increasing bendingstiffness and buckling resistance.

As noted above, cells 40 can utilize only the longer legs 300, only theshorter legs 400, a longer leg 300 combined with a shorter leg 400, or ashorter leg 400 combined with another shorter leg 400. This allows forcells 40 of at least four different heights.

FIGS. 6A-6C illustrate the top or deck 120 in further detail. Here, deck120 has recesses 500 corresponding in number and location to therecesses 200 of base 100. That is, the deck 120 has six recesses 500arranged in rectangular manner, with two rows of three recesses 500. Thedeck 120 has a rectangular shape, with recesses 500 located at eachcorner and two recesses 500 located at the midpoints of each longerside, where the outer edges of recesses 500 each protrude beyond thesides 506 of deck 120. However, the deck 120 is not limited to thisconfiguration, and may have any shape, and any number or position ofrecesses 500, so long as the recesses 500 are positioned to verticallyalign with the recesses 200 of base 100. Indeed, the deck 120 need notbe rectangular in shape, and need not be of the same general shape asthat of the base 100, even though the base 100 and deck 120 are shown aseach having a rectangular shape in the present embodiment. The recesses500 are holes that extend through the deck 120, and contain featuresallowing for snap fit (or other suitable attachment) to legs 300, 400.

The deck 120 also has stiffeners 502 arranged in diagonal manner betweenrecesses 500, as shown. The stiffeners 502 are bar- or beam-shapedstructures placed within channels formed in the deck 120, and connectedto the deck 120 at their ends. The stiffeners 502 can be made of thesame material as the deck 120, or may be made of a stronger materialsuch as a steel. The stiffeners 502 can be integrally formed with thedeck 120 or may be separate members attached to the deck 120. Connectionto the deck 120 can be made in any manner, such as by forming thestiffeners 502 integrally with the deck 120, snap fitting the stiffeners502 within appropriate features formed in the deck 120, attaching thedeck 120 and stiffeners 502 to pins that secure the deck 120 to thestiffeners 502, or the like. Any connection method or apparatus iscontemplated. The stiffeners 502 add to the strength and bendingstiffness of the deck 120. The body of the deck 120 is formed of ahoneycomb structure 504 for sufficient strength while saving weight andmaterial. It is contemplated that the cells 40 will often be filled withsoil first, then the deck 120 attached. However, and in the alternative,hexagonal holes of the honeycomb structure 504 are sized to allow soilto relatively easily fall through the deck 120 and into the space withinthe cell 40, allowing for the cells 40 to be filled with soil after thedeck 120 is attached. For example, in one embodiment, the hexagonalholes measure 30 mm across the diagonal, and 27.3 mm across the flats.In this manner, the cell 40 can be easily filled with soil even after itis fully assembled, by simply pouring soil on top of the deck 120 andallowing it to fall through the hexagonal holes and into the cell 40 (orperhaps working the soil slightly to allow it to fall through the deck120). The hexagonal holes are not limited to this particular shapehowever, and embodiments of the invention contemplate any sizes andarrangements of holes that allow soil to readily fall therethrough.

Embodiments of the deck 120 also have arched shapes, to better supportloads. For example, the upper and lower surfaces of deck 120 areslightly curved or arched, as shown in FIGS. 6B and 6C. Morespecifically, the upper surface has an arch or curve that extends acrossthe entire deck 120, with lowest points at the two opposing shortersides of the deck 120 and a highest point in the middle. Similarly, thelower surfaces are also curved or arched between adjacent recesses 500,with each curve or arch having lowest points at or near two adjacentrecesses 500, and highest points inbetween. Other embodiments need notinclude these arches or curved surfaces, or may include only some ofthem. Likewise, the degree or amount by which each surface is arched mayvary to any degree that allows the deck 120 to facilitate maintenance ofroot growth medium within cells 40 in a substantially uncompacted state.

As described above, the cells 40 are modular and designed to be usedwith legs of multiple lengths, allowing for cells 40 of multiple heightsfor use in many different applications. FIGS. 2A-2C, as alreadydescribed, illustrate a cell 40 constructed using a single set of longerlegs 300. Meanwhile, FIGS. 7A-7C illustrate a cell 40 constructed sothat each vertical support is made up of a longer leg 300 and a shorterleg 400 connected to each other, and FIGS. 8A-8C illustrate a cell 40constructed using a single set of shorter legs 400. The cells 40 ofFIGS. 2A-2C may be used in applications where an intermediate-sized cell40 is desired, such as, for example, when an intermediate amount ofuncompacted soil is desired, or when the particular site is sized sothat it can only accommodate intermediate-sized cells 40.

In FIGS. 7A-7C, each recess 200 has a longer leg 300 attached thereto,as above via a turn and lock mechanism or any other suitable mechanism.Attached to each longer leg 300 is a shorter leg 400, again attached viaa turn and lock mechanism or any other suitable mechanism. The shorterlegs 400 are then attached to recesses 500 of the deck 120, via snap fitor other appropriate mechanisms. The cells 40 of FIGS. 7A-7C thus employboth a longer leg 300 and a shorter leg 400 for each vertical support,and are therefore taller than those of FIGS. 2A-2C which employ only asingle longer leg 300. Accordingly, the cells 40 of FIGS. 7A-7C may beused in connection with larger sites that can accommodate larger cells40, when a large amount of uncompacted soil is desired, more stormwateris desired to be retained, or the like.

In FIGS. 8A-8C, each recess 200 has only a shorter leg 400 attachedthereto, again via a turn and lock mechanism or any other suitablemechanism. The shorter legs 400 are then attached to recesses 500 of thedeck 120, via snap fit or other appropriate mechanisms. The cells 40 ofFIGS. 8A-8C thus employ only a single shorter leg 400 for each verticalsupport, and are therefore shorter than those of FIGS. 2A-2C.Accordingly, the cells 40 of FIGS. 8A-8C may be used in connection withsmaller sites that can only accommodate these smaller cells 40, when arelatively small amount of uncompacted soil is desired, less stormwateris desired to be retained, or the like.

In operation, a foundation 60, which is typically impermeable to treeroots, can be formed. Often, the foundation 60 is soil which has beencompacted to at least 95% proctor to serve as an underlying foundationfor construction, as is known. However, the foundation 60 can be anyother layer that is highly resistant or effectively impermeable to treeroots, such as bedrock, concrete, aggregate, or the like. Then, a numberof cells 40 are assembled and placed side by side around the rootball ofa tree 10, as shown in FIG. 1. The tree 10 may already be present, orthe cells 40 may be arranged with a gap inbetween, and the rootball of atree 10 may be inserted into the gap. The number of cells 40 used ispreferably sufficient to provide enough volume of uncompacted soil toallow the roots of tree 10 to grow to their full natural capacity,although any number is contemplated. The cells 40 are not connected toeach other. Rather, they are simply placed side by side, and not coupledto each other. Indeed, it can be seen that the individual cells 40 haveno mechanism by which they can be attached or otherwise coupled to eachother.

The spacing between cells 40 may range. For example, depending on theapplication desired, adjacent cells 40 may be immediately adjacent toeach other, and perhaps even contacting (touching but not otherwisecoupled to) each other. At the other extreme, adjacent cells 40 may beplaced several inches or more apart from each other. Any intermediatepositions are also contemplated. As one nonlimiting example, adjacentcells 40 may be placed from 0 to 5 inches apart from each other. Asabove, this helps prevent the failure of one cell 40 from compromisingits adjacent cells 40, and also allows for easier repair of underlyingutilities, service lines, or anything else placed within or under thecells 40.

Next, soil or any other tree root growth medium is poured into the cells40 and evenly spread therethrough, after which the decks 120 are placedover the cells. In this manner, the cells 40 are filled withsubstantially uncompacted, or loosely compacted, soil. It may also bepossible to attach the decks 120 first then pour soil/growth medium overthe decks 120, where it falls through (or can be readily manipulated soas to fall through) the holes in the decks 120 to fill the empty spacewithin each cell 40.

Subsequently, a geotextile layer is typically placed upon the decks 120,and the aggregate 30 and hardscape 20 are poured upon the geotextilelayer. The weight of the aggregate 30 and hardscape 20 then acts to pushthe geotextile layer partially into the depressions 300. This acts tosecure the deck 120 and cells 40 against any lateral movement, adding tothe structural stability of the cells 40. Stability is further aided bythe soil 50, which also supports the cells 100 against any lateralmovement.

In the resulting configuration, one of ordinary skill in the art willobserve that the cells 40 support the weight of their overlyingaggregate 30, hardscape 20, and any traffic (foot or vehicle) thatpasses thereover. As the cells 40 support this weight, the tree growthmedium is left substantially uncompacted, supporting only its ownweight. Accordingly, the rootball of tree 10 is surrounded with asignificant volume of substantially loosely compacted soil, which allowsthe roots of tree 10 to grow therethrough, providing space and asuitable medium for the roots to grow to their full natural sizerelatively unencumbered. This is in contrast to many conventional urbantree growth sites, which are surrounded by hardscape such as concreteroads and sidewalks that require their underlying earth to be packed sodensely and solidly to support the hardscape, that tree roots cannotgrow therethrough, thus stunting their growth as well as that of thetree. Thus, embodiments of the invention allow for growth of large treesin areas where they could not be grown before, in particular dense urbanareas containing significant hardscape covering. This also allows formuch more stormwater retention in these areas, which is a significantadvantage over conventional dense urban areas, whose hardscape coveringtypically converts most stormwater to relatively useless runoff thatalso contributes to problems such as flooding and the like. Instead ofsimply producing runoff, embodiments of the invention retain stormwater,using it to water trees and provide other benefits, while also reducingthe problems commonly associated with runoff, such as flooding.

Retention of stormwater also provides further benefits, such aspollutant removal and cleaning of runoff water. More specifically, boththe loosely compacted soil and tree roots clean and/or filter water thatthey capture. Accordingly, instead of simply producing runoff thatbecomes contaminated as it picks up impurities and chemicals from theground, embodiments of the invention retain and clean stormwater so thatit can be used in tree or plant growth, etc.

In terms of specific numbers, since the cells 40 support substantiallythe entire weight of overlying hardscape, aggregate, and commercialtraffic, the soil or root growth medium does not experience anycompressive force except that of its own weight. Accordingly, the cells40 can maintain the soil or root growth medium in an uncompacted state,e.g., at approximately 80% proctor or less (roughly corresponding tocompaction by human foot, or less). In contrast, the hard-packed soilcreated by general construction is typically 90-95% proctor or so, whichis known to be effectively impenetrable to tree roots. Trees planted intypical construction sites, such as under pavement supported byhard-packed soil, commonly only have a small area in which to grow roots(usually a small volume dug out from the hard-packed soil of aconstruction area), resulting in a stunted root system and a smaller,less healthy tree. In contrast, the cells 40 of embodiments of theinvention allow for large areas of substantially uncompacted, or looselycompacted, soil to exist even under or next to construction sites andother areas of hard-packed soil, resulting in growth of large, healthytrees even in areas that could not conventionally support such trees,like dense urban areas covered by concrete or asphalt.

As above, such cells 40 are largely open, indeed having up to 90% ormore of their volume being free volume available to be taken up by rootgrowth. The significant amount of open area within cells 40 also allowsfor other structures to extend therethrough. For example, water pipes,electrical or other lines may be run into or through the cells 40, sothat utilities need not be routed around any system of cells 40.

Attention now turns to further features of the cells 40 of embodimentsof the invention. In some though not all applications, it is desirablefor the bases 100 and decks 120 to be stackable upon each other, so thatthe bases 100 and decks 120 can be more readily and more efficientlytransported. FIGS. 9A-9C illustrate stacked bases 100 configuredaccording to an embodiment of the present invention. Here, the recesses200 of each base 100 have rims 600 extending upward, out of the mainbody of their base 100. The rims 600 can extend upward to any distance(i.e. each can have any height), but in one embodiment can be sized toprovide protection to the joints between their recesses 200 and legs300/400, as well as provide sufficient clearance between stacked bases100, without providing excessively large clearance between stacked bases100 and thus reducing the efficiency and compactness with which they canbe stacked.

Each recess 200 can also have a corresponding circular depression oropening 610 formed on the other side of the base 100 as the rim 600, andsized to hold the rim 600 of another base 100. In this manner, the rims600 of one base 100 may engage with the openings 610 of another base 100that is stacked on top, holding it securely in place. Thus, stackedbases 100 can be coupled together in lateral directions (i.e. kept fromsliding laterally off of each other, and thus remaining stacked), butsubstantially uncoupled in the vertical direction. That is, the base 100at the top of the stack is kept from sliding laterally off of the stack,but is free to be removed from the stack simply by lifting it off.

The recesses 200 may or may not be present, and the invention includesembodiments in which they are, as well as embodiments in which they arenot. In high loading situations where recesses 200 are desired, therecesses 200 and surrounding material of the base 100 may be reinforced,such as by thickening the walls of these structures, addingreinforcement, or the like.

Embodiments of the present invention may also include stackable decks120. FIGS. 10A-10C illustrate stacked decks 120 configured according toan embodiment of the present invention. Here, the recesses 500 have rims700 extending downward, away from the main body of their deck 120. Therims 700 can extend downward any distance, i.e. each can have anylength, but in one embodiment can be sized to provide protection for thejoints between recesses 500 and the tops of legs 300/400, as well asprovide sufficient clearance between stacked decks 120. Conversely, therims 700 are made short enough to avoid excessively large clearancebetween stacked decks 120, which would reduce the efficiency andcompactness with which they can be stacked.

Each recess 500 can also have a corresponding circular depression oropening 710 formed on the upper surface of the deck 120 (i.e. on theother side of the deck 120 as the rim 700). The rims 700 of one deck 120may thus engage with the openings 710 of another deck 120 that isstacked below, thus holding it securely in place. Like the bases 100,the decks 120 when stacked can thus be coupled together in lateraldirections (i.e. kept from sliding laterally off of each other, and thusremaining stacked), but substantially uncoupled in the verticaldirection. That is, the deck 120 at the top of the stack is kept fromsliding laterally off of the stack, but is free to be removed from thestack simply by lifting it off.

It should be noted that the above described cells 40 and their variouscomponents may be made of any materials, and may be of any specificdimensions, that allow the cells 40 to support overlying hardscape andits commercial vehicle traffic while maintaining the soil within thecells 40 in a substantially uncompacted state and allowing forrelatively unimpeded tree root growth therethrough. That is, the cells40 must be sufficient to support the weight of the overlying hardscapeand commercial vehicle traffic by themselves, while transferring littleto none of this weight to the soil within, while also being large andopen enough to allow for relatively unimpeded growth of tree rootswithin. Any such materials and dimensions that allow for this to happenare contemplated.

As one nonlimiting example, the various components of cells 40 may havecertain specific dimensions as follows. The base 100 may measure600×1200 mm, and the height as measured from the bottom of base 100 tothe top of a rim 600 may be 110 mm. The deck 120 may have similarmeasurements (in one case, 592×1193×107 mm). Longer legs 300 may be 725mm in length, 160 mm in diameter at their lower end, 158 mm in diameterat their upper end, and 153.7 mm in diameter at their central portionand as measured from the center of one longitudinal protrusion 320 toits opposite protrusion 320. The nominal wall thickness of longer legs300 may be 3.175 mm, and the upper and lower portions may each beapproximately 100 mm in length. Similarly, shorter legs 400 may be 365mm in length, with the remaining dimensions being the same as those oflonger leg 300.

One of ordinary skill in the art will realize that, for these and otherdimensions, the base 100, longer legs 300, and shorter legs 400 may bemade of injection molded high density polyethylene (HDPE), with the deck120 made of a stronger material like a glass-filled resin. Thisglass-filled resin may be a 30% glass-filled polypropylene, or any othermaterial of similar or greater strength. This is in contrast to priordesigns such as those of U.S. Pat. Nos. 7,080,480 and 8,065,831, whichboth utilized 30% glass-filled polypropylene or stronger material fortheir entire cells, rather than the cheaper HDPE. Accordingly,embodiments of the present invention allow for significant cost savingsin materials, as cheaper HDPE is used for a large portion of the cells40. One of ordinary skill in the art will also realize that theinvention is not limited to these dimensions or these materials, andinstead contemplates any dimensions, and any corresponding materials,that lead to a cell that is capable of supporting overlying hardscapeand its commercial vehicle traffic while maintaining the soil within ina substantially uncompacted state and allowing for relatively unimpededtree root growth therethrough.

The above and other embodiments are configured to support the weight ofoverlying hardscape (e.g. a standard concrete or asphalt roadway,pavers, etc.) and aggregate that cover the entire upper surface of thecell, as well as commercial vehicle traffic (e.g., trucks, cars,emergency vehicles, and any other vehicles commonly found on roadways)thereover, to a degree at least equivalent to an H-20 loading condition.For example, the above and other embodiments can support a load of atleast 21.0 psi when the hardscape 20 is pavers with concrete, and atleast 15 psi when the hardscape 20 is just pavers.

As noted above, one notable advantageous application of cells 40 isstormwater management. As one example, cells 40 can be used to create aponding area for storing rainwater runoff. In such an application, anumber of cells 40 may be placed (not necessarily side by side) underhardscape, and may or may not be filled with soil. Trees 10 also may ormay not be present. Ingress and egress for water are provided, such as arunoff drain or simply an open area in the overlying hardscape, as wellas an underdrain that may extend into the volume outlined by cells 40 toconvey excess water somewhere else, such as to a primary stormwatersystem.

Another application of cells 40 is that of underground bioretentionsystems. A bioretention system, sometimes referred to as a rain garden,is typically a volume of soil and/or other materials used to collect andhold runoff water, and remove pollutants therefrom. Stormwater istypically collected into a treatment area, which is an area of groundcontaining different layers such as a grass strip, sand bed, one or moreorganic layers, soil, and plants. These layers collect the runoff water,filter and aerate it, support the growth of microorganisms which breakdown certain undesired compounds in the runoff water such ashydrocarbons, and absorb other undesired compounds. The “cleaned” runoffwater then gradually propagates into the soil surrounding thebioretention system, evaporates away, or can be removed for useelsewhere. The cells 40 can create such a bioretention systemunderground. For example, the configuration of FIG. 1 can be filled notwith solely conventional soil as in some above-described applications,but with layers that constitute a bioretention system. As above, suchlayers can include a sand bed, one or more organic layers, soil of anytype, or the like. Embodiments of the invention encompass any materiallayers suitable for use in a bioretention system. Ingress and egress forrunoff water may also be added if desired, such as drains or pipes thatconvey water into and out of the cells 40.

Runoff water is thus channeled into the cells 40, where the variouslayers as well as the roots of tree 10 filter, aerate, and break downpollutants in the water. The water is then taken up by the tree 10,evaporates, enters the surrounding soil, or is removed by the wateregress. In this manner, cells 40 of embodiments of the invention can bedeployed to create an underground bioretention system that serves thedual purpose of supporting tree growth and has the added advantage ofutilizing the tree and its root system to improve the function of thesystem.

It should be noted that bioretention systems formed utilizingembodiments of the present invention offer significant advantages overconventional bioretention systems. For example, conventionalbioretention systems are known to degrade over time. In contrast, it hasbeen found that bioretention systems constructed according toembodiments of the present invention actually improve over time. Inparticular, as the trees within it grow larger and more mature rootsystems, the larger root system absorbs more water and removes morepollutants. It has also unexpectedly been found that the benefitimparted to bioretention systems by incorporating trees within is agreater than linear benefit. That is, such systems improve in greaterthan linear manner as a function of tree growth, with larger treesoffering much more benefit (water absorption and pollutantabsorption/breakdown) than smaller ones.

It should further be noted that these above mentioned advantageousembodiments all come with the further benefit of more efficient landuse. The structural cells 40 are all sufficient to support conventionalhardscape above. Thus, all of the above advantageous embodiments can beimplemented belowground without compromising any of the conventionalstructures or systems aboveground. For example, bioretention systems,stormwater retention systems, and the like can all be implementedunderneath sidewalks and streets, so that they do not reduce the amountof parking spaces available. Larger trees can be grown without reducingthe amount of sidewalk available for walking. In this manner, the abovedescribed advantages can be accomplished without reducing theaboveground real estate available for conventional uses.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the invention.However, it will be apparent to one skilled in the art that the specificdetails are not required in order to practice the invention. Thus, theforegoing descriptions of specific embodiments of the present inventionare presented for purposes of illustration and description. They are notintended to be exhaustive or to limit the invention to the precise formsdisclosed. Many modifications and variations are possible in view of theabove teachings. For example, the cells 40 can take on any shape besidesrectangular, and can have any number of vertical supports, each of whichcan contain any number and combination of legs. The cells 40 can also bemade of any material or materials sufficient to allow cells 40 tosupport overlying aggregate and hardscape as well as traffic loading.The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as are suited to theparticular use contemplated. Additionally, different features of thevarious embodiments of the present invention, disclosed or otherwise,can be mixed and matched or otherwise combined so as to create furtherembodiments contemplated by the invention.

What is claimed is:
 1. A single-layer system of structural cellssubstantially uncoupled in the vertical direction for supportinghardscape, allowing tree root growth, and managing stormwater underneaththe hardscape, the system comprising: a base comprising a plurality ofreceptacles and a plurality of support members interconnecting thereceptacles; a plurality of legs; and a top attachable to the legs;wherein the plurality of legs affixes the base to the top, and whereinthe plurality of legs comprise different lengths; wherein the base, thetop, and the legs attached thereto define a volume, and are configuredto support at least that portion of the hardscape overlying the top aswell as a commercial vehicle traffic load thereon, while maintaining atleast approximately ninety percent of the volume as free volume which isfree of structural material; and wherein the free volume is available tobe filled with uncompacted soil, tree roots, utilities, stormwater, orcombinations thereof.
 2. The structural cell system of claim 1, whereinouter edges of the receptacles extend beyond outer edges of the supportmembers.
 3. The structural cell system of claim 1, wherein the base andthe legs each comprise an unreinforced plastic.
 4. The structural cellsystem of claim 3, wherein the unreinforced plastic is high densitypolyethylene (HDPE).
 5. The structural cell system of claim 1, whereinthe base, the top, and the legs attached thereto are sized and shaped tosupport a load of at least approximately 15 psi across substantially theentire top.
 6. The structural cell system of claim 1, wherein: at leasttwo of the receptacles lie along a first direction, and at least two ofthe receptacles lie along a second direction different from the firstdirection; and each of the legs has a cross-sectional shape havingprotrusions, the protrusions arranged so that, when each of the legs isattached to a receptacle, its protrusions extend in the first and seconddirections.
 7. The structural cell system of claim 1, wherein theplurality of legs comprise at least one pair of legs and at least oneadditional pair of legs.
 8. The structural cell system of claim 7,wherein the at least one pair of legs comprises two legs having the samefirst length, wherein the at least one additional pair of legs comprisestwo legs having the same second length, and wherein the second length isshorter than the first length.
 9. The structural cell system of claim 1,wherein one base, a set of the legs, and one top are attachable to eachother to collectively form a structural cell, the structural cellconfigured so that plural ones of the structural cells are substantiallyuncoupled to others of the structural cells positioned along a lateraldirection.
 10. The structural cell system of claim 1, furthercomprising: a bioretention system positioned within the structural cellsystem; and tree roots extending into the bioretention system, the treeroots being from a tree positioned proximate to the structural cellsystem.
 11. The structural cell system of claim 1, wherein the base, theassociated legs, and the top collectively comprise a single structuralcell, and wherein the structural cell has no mechanism for coupling toanother one of the structural cells.
 12. The structural cell system ofclaim 1, wherein the outer surface of each leg further comprises one ormore rounded protrusions extending outward from a central axis of theeach leg.